1. Field of the Invention
The present invention relates to a pipe joint for hermetically connecting fluid pipelines, in such a manner that the relative angle therebetween can vary, by means of a ring-shaped sealing ring.
2. Description of the Related Art
Conventionally, exhaust systems for automotive vehicle have been devised in such a manner that the connection between the combining pipe of the exhaust manifold and an exhaust pipe, and connections between exhaust pipe and exhaust pipe, are capable of variation in the relative angle between pipes by means of a pipe joint having the composition described below, in order to suppress relative movement between the vehicle and engine, or the like, occurring due to vibration of the engine or vibrations from the road surface whilst the vehicle is moving.
For example, in a widely used composition such as the pipe joint 50 illustrated in FIG. 6, a tapered sealing seat 52b is formed on the inner circumference of an integrated flange 52 formed on the downstream end portion of the combining pipe 51 of an exhaust manifold provided in the engine of an automotive vehicle, and furthermore, a ring-shaped sealing ring 54 having a convex surface 54a corresponding to the aforementioned sealing seat 52b is installed on the outer circumference of the connecting end portion 56 of an exhaust pipe 53 connected to the aforementioned exhaust manifold 51 [sic], the aforementioned tapered sealing seat 52b and the aforementioned convex surface 54a being capable of hermetic sliding motion such that the relative angle therebetween can vary, under pressure applied by pressure connecting means 55 provided in the coupling region between the two pipelines.
Moreover, with regard to pipe joints for connecting together two exhaust pipes in an automotive vehicle, the spherical pipe joint disclosed in Japanese Patent Publication No.(Hei)2-33912 is known, for example. This joint is composed in such a manner that a ring-shaped sealing ring having a convex surface is installed on the outer circumference of the end portion of an upstream-side exhaust pipe, and a flange having a concave-shaped sealing seat corresponding to the aforementioned convex surface formed therein is fixed by welding to the connecting end portion of a downstream-side exhaust pipe, the convex surface of the aforementioned ring-shaped sealing ring and the concave surface of the aforementioned sealing seat being capable of hermetic sliding motion such that the relative angle therebetween can vary, under pressure applied by pressure connecting means provided in the coupling region between the two exhaust pipes.
The ring-shaped sealing rings used in conventional pipe joints of these kinds are generally obtained by overlaying a fire-resistant material in sheet form, such as expanded graphite or mica, for example, with fine metal wire made from stainless steel, or the like, winding and laminating same, and then applying strong pressure to the laminate surface from a perpendicular direction in a metal mould of a prescribed shape, thereby forming a truncated spherical shape having a cylindrical hole in the centre thereof. However, since the aforementioned fine metal wire has high elasticity, it has been difficult to ensure adequate precision in the moulding of the concave surface formed in the ring-shaped sealing rings.
Moreover, in order to ensure good sealing properties between the ring-shaped sealing ring and the outer circumference of the connecting end section, thereby preventing any leakage of exhaust, the ring-shaped sealing ring installed on the outer side of the aforementioned connecting end section is held under strong pressure by means of a fastening spring, and consequently the related installation task is complicated and leads to an increase in costs.